The present invention relates to a titanium dioxide product suitable for incorporation into ceramic frit, and to a method for preparation of the titanium dioxide.
Commercially available pigmentary-TiO.sub.2 cannot normally be utilized in the preparation of ceramic frit, due to the fact that this type of TiO.sub.2 has a very small particle size and consequently a very large surface area which causes the formation of large agglomerates when all of the component ingredients of the ceramic frit are dry blended. These TiO.sub.2 agglomerates possess a higher density and a higher melting point than the remainder of the frit ingredients and there is therefore a tendency for unmelted TiO.sub.2 to sink to the bottom of the melt. This results in low TiO.sub.2 content in the melt and non-uniform distribution of the TiO.sub.2. If, however, the TiO.sub.2 consists of larger discrete particles having relatively less surface area and less tendency toward agglomeration, the lower melting components of the frit aid in complete solution and melting of the TiO.sub.2.
The following patents are illustrative of the prior art: U.S. Pat. No. 3,403,977 (Heywood) discloses a process for a TiO.sub.2 product suitable for ceramic frit, which consists of modules which in turn are made up of aggregates of TiO.sub.2 particles.
U.S. Pat. No. 3,211,528 (Wiggington) discloses a process for hydrolysis and calcination of a TiO.sub.2 product for use in ceramic frit. This process involves a Blumenfeld-type hydrolysis, wherein the hydrolysis seed is formed in situ by adding liquor to water rather than by addition of already-formed nuclei. The resulting product is described as being free flowing and non-dusting, but it also involves a process wherein a significant portion of the hydrolysate must be neutralized, freed from its sulfate content, and treated with a peptizing agent prior to recombination with the major portion of the material before calcination is carried out.